Obesity is defined as the excessive accumulation of body fat. A body weight 20% over that in standard height-weight tables is arbitrarily considered obesity (except for certain heavily muscled persons).
The prevalence of obesity in the U.S.A. is 24% of men and 27% of women. There are great differences in age, socioeconomic status, and race. For example, there is a two fold increase in the prevalence of obesity between the ages of 20 and 55. Obesity is also far more common among black than white women, reaching a value of 60% among middle-aged black women ("The Merck Manual of Diagnosis and Therapy", Berkow et al., 16.sup.th Edition, 1992, Merck Research Laboratories).
Obesity and overweight are largely genetically determined and are strongly conditioned by available palatable food and sendentariness. A child of two obese parents has about 80% chance of becoming obese, whereas that risk is only 15% for a child of two normal weight parents. Twin and adoption studies have also shown that genetic factors are critical determinants of obesity.
Endocrine and metabolic factors can also be associated with developing and maintaining obesity, e.g., adipose tissue proliferation in hyperadrenocorticism is due to corticosteroid excess and leads to increased gluconeogenesis and a correspondingly greater demand for insulin, which, in turn, stimulates lipogenesis.
Obesity has numerous medical consequences. These vary depending on the severity of obesity. Severely obese individuals (weighing 60% over a normal weight) have a high risk of developing cardiorespiratory problems. They are also at risk of developing chronic hypoventilation, which can lead to hypercapnia, pulmonary hypertension, and heart failure. Severe episodic hypoxia can cause arrhythmias and sudden death is 10 times more common in the severely obese. Severely obese individuals are also at increase risk of suffering from obstructive sleep apnea, pickwickian syndrome (i.e., daytime hypoventilation, somnolence, polycythemia, and cor pulmonale), and renal vein thrombosis. In addition, a severely obese individual suffers psychological consequences of the disorder ("Cecil Essentials of Medicine", Andreoli et al., Third Edition, 1993, W.B. Saunders Company).
Moderate obesity (corresponding to a weight between 20-60% above normal weight) poses increased risk of early mortality. Obese individuals suffer more frequently than non obese individuals from hypertension. Type II diabetes mellitus can also be aggravated by excess weight. Obesity also increases the risk of cholelithiasis and endometrial carcinoma.
Obesity is often associated with high triglyceride and low high density lipoprotein (HDL) concentrations and thus renders an obese subject susceptible to cardiavascular diseases, such as ischemia, restenosis, congestive heart failure, and atherosclerosis.
The availability of a test allowing to predict whether a person is at risk of becoming obese would greatly enhance prevention and treatment of obesity and thus of the multiple medical consequences resulting from obesity.